Differential mitochondrial dinitrosyliron complex formation by nitrite and nitric oxide

Nitrite represents an endocrine reserve of bioavailable nitric oxide (NO) that mediates a number of physiological responses including conferral of cytoprotection after ischemia/reperfusion (I/R). It has long been known that nitrite can react with non-heme iron to form dinitrosyliron complexes (DNIC). However, it remains unclear how quickly nitrite-dependent DNIC form in vivo, whether formation kinetics differ from that of NO-dependent DNIC, and whether DNIC play a role in the cytoprotective effects of nitrite. Here we demonstrate that chronic but not acute nitrite supplementation increases DNIC concentration in the liver and kidney of mice. Although DNIC have been purported to have antioxidant properties, we show that the accumulation of DNIC in vivo is not associated with nitrite-dependent cytoprotection after hepatic I/R. Further, our data in an isolated mitochondrial model of anoxia/reoxygenation show that while NO and nitrite demonstrate similar S-nitrosothiol formation kinetics, DNIC formation is significantly greater with NO and associated with mitochondrial dysfunction as well as inhibition of aconitase activity. These data are the first to directly compare mitochondrial DNIC formation by NO and nitrite. This study suggests that nitrite-dependent DNIC formation is a physiological consequence of dietary nitrite. The data presented herein implicate mitochondrial DNIC formation as a potential mechanism underlying the differential cytoprotective effects of nitrite and NO after I/R, and suggest that DNIC formation is potentially responsible for the cytotoxic effects observed at high NO concentrations.